High current (6kA) LV s/b question
High current (6kA) LV s/b question
(OP)
If I wanted to run 3 + (1 backup) 1MW 415V generators into a single output, I would expect to have 4 2000A c/b's bussed using copper bar to a single 6300A circuit breaker that would provide the feed out (with OCR's set to correct levels obviously). Even if it was aligned with the 6300A breaker in the middle, and a pair of 2000A's either side, it would need to be a fairly hefty and type-tested bar system to give enough guaranteed kA rating to suit 4 generators, presumably due to skin effect + EM forces.
Is there a reason why you cannot cable the 2000A breakers back to the 6300A, cores in trefoil? Provided you take into account all de-rating variables in the installation, and size the number and type of cables / phase appropriately, wouldn't that be better for s/c withstand?
Not an engineer, just a licensed sparky, but curious.
Is there a reason why you cannot cable the 2000A breakers back to the 6300A, cores in trefoil? Provided you take into account all de-rating variables in the installation, and size the number and type of cables / phase appropriately, wouldn't that be better for s/c withstand?
Not an engineer, just a licensed sparky, but curious.






RE: High current (6kA) LV s/b question
That 6300A breaker will rely on the busbars acting as a heatsink to conduct heat away from the main disconnects, which is reason why it wouldn't be practical.
RE: High current (6kA) LV s/b question
6300A rated switchboards (with suitable fault ratings) are available but are normally connected using busducts rather than cabling, but why would you want to collate the output of 4 gensets into one breaker rated @6300A? You would presumably then be connecting the 6300A output breaker to a 6300A incomer on another switchboard. Why not just have a switchboard with 6300A rated bars and your 2000A breakers taking the inputs from the gensets, with suitably rated output breakers on the same bar then feeding your loads?
Am I missing something?
RE: High current (6kA) LV s/b question
ppedUK: Not uncommon to gang a few generators together to provide a single feed out to a step up transformer, because at short notice you might not be able to get a 11kV genset, where as 415V 1250kVA containerised units are common as dirt, and so are transformers. My question was more along the lines of, why can't you use cable instead of busbar?
RE: High current (6kA) LV s/b question
I agree with ppedUK, there's almost certainly a reason why this isn't done.
RE: High current (6kA) LV s/b question
The short-circuit will be supplied by all generators- or at least of 3 of 4-50 to 63 kA, I guess.
In my opinion-as already said-a trefoil arrangement hold by suitable cleats each meter would be o.k. However you may calculate the forces according to IEC 60865-1 Short-circuit currents – Calculation of effects [Section 2 The electromagnetic effect on rigid conductors and flexible conductors ch.2.3.Flexible conductor arrangements].Since the main scope of this section it is the overhead line only formula 19 is significant for cables.
I think, nevertheless, you have to employ Ipeak value instead of I”k3- as shown there.
You may also consult IEC 61914 Cable cleats for electrical installations.
The cleat [or clamp] catalogue presents also the maximum permissible force in order to choose the suitable one.
See [for instance]:
http://www.id-technik.com/en/start/
http://www.id-technik.com/fileadmin/site/documents...
RE: High current (6kA) LV s/b question
Bill
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"Why not the best?"
Jimmy Carter
RE: High current (6kA) LV s/b question
I think you may be missing a zero or two in there. 1600 kVA perhaps? Or one of those 600kW sets?
RE: High current (6kA) LV s/b question
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: High current (6kA) LV s/b question